Wireless technology: RF modules rule the Waves.

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Every electronic product seems to come with a wireless link. My neighbor's sprinkler system includes a wireless unit that lets him sit indoors and program his watering times and sequences. A variety of chips and modules from many manufacturers makes it easy for engineers to drop a wireless link into new and existing designs. Many of those devices conform to the IEEE-802.15.4 specification for a wireless personal-area network (WPAN) that accommodates low data rates, short-range communications and low-power operations. But in some cases, non-standard chips and modules work just as well.

Some confusion surrounds the 802.15.4 standard which specifies a radio or "physical layer" that communicates information. The popular ZigBee protocol, for example, builds upon radios that comply with the 802.15.4 standard. ZigBee requires a stack that defines how applications communicate. Keep in mind that ZigBee and 802.15.4 are not the same (Figure 1). Protocols other than ZigBee can use 802.15.4 radios, too. (The ZigBee stack is much like the TCP/IP stack; a series of software layers that separate hardware from application programs.)

Anyone can obtain and use a ZigBee stack which comes built into some radios. But, that does not guarantee interoperability with ZigBee devices from other vendors. So far, the ZigBee Alliance developed one standard profile for the makers of home-automation products. Companies that use that profile can offer devices such as thermostats and switches that communicate with each other. Engineers in other industries are on their own when it comes to compatibility between products. Depending on the end application, proprietary communication products and protocols that use 802.15.4 radios can work as well as, or better than, those that use ZigBee.

Engineers can choose from a wide variety of chips, modules, development kits, software tools and related products that provide ZigBee or proprietary-communication protocols. We will cover some products and companies and list others in the "Wireless Chip and Module Resources" list that accompanies the longer Web version of this article at www.ecnmag.com. Under June 2007, click on "Cover Story."

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ZigBee Spreads a Wide Net

Radios in a typical ZigBee mesh network cover a large area and communicate over many radio-to-radio hops. Networks can take many configurations, as shown in Figure 2. "You find a mesh network in meter-reading systems," said Rodger Richey, senior applications manager in the Advanced Microcontroller Architecture Division at Microchip Technology. "Energy, water and gas meters would 'talk' to each other and relay messages to a main data-collection point."

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"You could find ZigBee in a home-control system that includes 10 to 12 nodes such as light switches," noted Richey. "ZigBee supports over 64,000 nodes, so the protocol comes with a lot of code that maintains routing tables and other protocol information. A typical ZigBee stack requires from 64 to 96 Kbytes and some stacks reach 128 Kbytes, so even a simple ZigBee-compatible light switch could require a large and expensive MCU. In some cases, ZigBee may be overkill."

To assist engineers with small networks, Microchip developed its own protocol stack called MiWi--basically, a "thin" media-access-control (MAC) layer that works with an 802.15.4 radio. The MiWi stack takes about 4 Kbytes of memory which lets it run in PIC16 MCUs. The protocol operates with up to 1,000 nodes in star, tree and mesh networks, and messages can make as many as four node-to-node hops. …

RF Monolithics, Inc. (RFM), a provider of M2M wireless technology, has introduced the ZPM3570 2.4 GHz ZigBee Pro module at the Embedded Systems Conference (ESC) 2011 in Silicon Valley. In a release, the Company said that its small size, 1MB data logging flash memory, and ZigBee Smart Energy and…

ZigBee devices are moving up in integration and down in cost, signaling a potential take-off for the wireless networking technology. Ember Corp. is ramping up production of what it says is the first single-chip ZigBee solution, as well as its second-generation ZigBee software stack, EmberZNet 2.0.…

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